255/40 R19 vs 255/45 R18

What changes when you change tire size?

255/45 R18 stays within the configured tolerance for 255/40 R19: 0.0% diameter and 0.0% speedometer effect.

Geometric comparison

Geometric comparison
Metric This size: 255/40 R19 Alternative: 255/45 R18 Difference Verdict
Overall diameter 27.03 in 27.04 in 0.0% Within tolerance
Section width 10.04 in 10.04 in 0.00 in Computed difference
Sidewall height 4.02 in 4.52 in +0.50 in Computed difference
Circumference 84.92 in 84.93 in 0.0% Within tolerance
Speedo 0.0% 0.0% 0.0% Within tolerance

Compare sizes

Looks valid
Looks valid
Units
Editorial preset

These are TireFitLab editorial diameter-screening presets. Regional names choose a preset, not a national legal limit, ETRTO rule or vehicle approval. The AWD preset does not establish an allowable drivetrain mismatch. Use the exact vehicle and tyre manufacturer instructions; nominal geometry alone cannot approve fitment.

Requires verificationWithin tolerance · Diameter +0.0% (+0.00 in) · US preset (±3%)
  • Requires verification · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter +0.0% · Ride-height change +0.00 in.
  • Speedometer unchanged · 60 mph → 60.0 mph.
  • Sidewall +0.50 in · Width +0.00 in.
Diameter+0.0%+0.00 in
Speedo @ 60+0.0%60 mph → 60.0 mph
Sidewall+0.50 inWidth +0.00 in
Ride-height change+0.00 inDiameter ÷ 2
How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check vehicle placard approval, load/speed rating, rim-width range, wheel-arch, suspension or brake clearance.

Methodology

Before fitting

  • Check the vehicle placard and owner’s manual first.
  • Match or exceed the required load index and speed rating.
  • Confirm rim-width range, bolt pattern, hub bore, offset and fasteners.
  • Inspect wheel-arch, suspension and brake clearance under real vehicle load.
  • Check TPMS, cold pressure and local roadworthiness rules.
Diameter
27.03 in 27.04 in+0.00 in
Sidewall
4.02 in 4.52 in+0.50 in
Width
10.04 in 10.04 in+0.00 in
Circumference
84.92 in 84.93 in+0.0%
Revs / mile
746 746
Speedo @ 60
60 mph 60.0 mph+0.0%
Ride-height change
0.00 in +0.00 in
True distance per 100 indicated
100 mi 100.0 mi+0.0%
Δ⌀ +0.00 inΔ↔ +0.00 in
  • Current — 255/40 R19
  • New — 255/45 R18
  • Grounded to the road: the axle rises +0.00 in.

Tires and wheels in one comparison

Result report

255/40 R19 255/45 R18 · Requires verification · Within tolerance

Plan budget for this size: 255/45 R18

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Plan budget for this size
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Estimated budgetBudget$100–$140Per tireMid-range$130–$185Per tirePremium$185–$260Per tire

Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.

In-tolerance alternative sizes

In-tolerance alternative sizes
SizeDiameterSpeedo @ 100Use this
−1″ 245/45R18-1.3%-1.3%
OE 255/40R19+0.0%+0.0%
+1″ 265/35R20+1.0%+1.0%
+2″ 265/30R21+0.8%+0.8%

255/40 R19 · 255/45 R18 · Methodology